appdata: do not use generic name "Hitori"

In a software center like GNOME Software, we should display the more
specific name "GNOME Hitori" rather than the generic "Hitori" that we
show once we're installed.

https://bugzilla.gnome.org/show_bug.cgi?id=731308
appdata: add to GNOME project group

Some software centers, like newer versions of GNOME Software, will use
this to associate Hitori with other GNOME apps.

https://bugzilla.gnome.org/show_bug.cgi?id=731308